EP3148745B1 - Honing process for fine machining of bores - Google Patents

Description

AREA OF APPLICATION AND PRIOR ART

The invention relates to a honing method for fine machining an inner surface of a bore in a workpiece.

Preferred field of application is the machining of substantially cylindrical sliding bearing surfaces in components for engine construction, in particular the machining of cylinder surfaces of an engine block or the processing of connecting rods in connecting rods.

Classical honing is a machining process with geometrically indeterminate cutting edges, in which a multi-bladed honing tool executes a two-component cutting movement, which leads to a characteristic surface structure of the machined inner surface. Usually, but not always, a surface structure with crossed processing marks (cross-cut) is aimed for. The working movement of the honing tool in the workpiece usually consists of an axially reciprocating stroke movement and one of these superimposed rotary motion. By honing finished surfaces can be produced, which meet extremely high requirements in terms of dimensional and form tolerances and in terms of the surface structure. Accordingly, in engine construction, for example, cylinder surfaces, i. Inner surfaces of cylinder bores in an engine block or in a cylinder sleeve to be installed in an engine block, subjected to bearing surfaces for shafts and the cylindrical inner surfaces in connecting rods honing.

Tolerances require holes to have a particular position in a workpiece-related coordinate system. The term "position" here refers to a three-dimensional position of the holes, i. both the local position of a bore and the angular position and the orientation of the bore in the coordinate system of the workpiece. The position of the bore may be e.g. be represented by the position of the bore axis.

Some of the pre-honing processes usually create holes whose position does not match the target position. The task of downstream machining operations is then to correct the position of the hole towards the desired position.

To prepare the workpieces to be machined for honing honing is often preceded by pre-machining by fine boring (also called fine turning or fine spindles), ie a machining with a geometrically defined cutting edge. The fine boring can be designed as position-correcting or position-determining fine boring operations to set the desired position of the bore. This can be traced in subsequent honing operations with a gimbal or otherwise limited movably mounted honing the specified by the fine boring hole axis without changing the position. An essential task of the honing operation is then the generation of the required surface roughness, the cylindrical shape and the diameter.

There are also suggestions to move the position of the hole by honing and thereby adjust. From the patent DE 103 48 419 C5 is a honing process for Schrupphonen the lateral surface of a bore in the partial section by a honing tool with honing stones on a cantilevered work spindle known. The term "roughing" stands for a honing with relatively strong material removal. The honing tool is positioned with its longitudinal axis at the desired position of the bore and inserted centrally to the desired position of the bore in the bore. The longitudinal axis of the work spindle is therefore offset from the longitudinal axis of the bore before honing eccentric to the bore. During the honing operation, material removal in the bore is performed such that displacement of the longitudinal axis of the bore occurs until any deflection that has occurred has been eliminated and the longitudinal axis of the completed bore is coaxial with the longitudinal axis of the work spindle. Thereafter, in the coaxial position of the longitudinal axes, the lateral surface is honed uniformly by roughing in full section. In order to increase the rigidity of the arrangement, a slide unit for a certain portion of the method is locked with the work spindle in the longitudinal direction of the work spindle such that the lifting movement of the honing tool is performed by the carriage unit so that the work spindle moves from the slide unit alternately with respect to its longitudinal axis becomes.

The positional displacement of the bore axis is effected here via a more or less rigid or rigid design of honing machine, spindle and honing tool. The desired nominal position is approached exactly, the rigidity in honing machine, work spindle and honing tool causes the drilling position of the tool position and thus the desired position approaches during the machining process.

The DE 10 2010 010 901 A1 describes honing method for honing crankshaft bearing bores. In this case, a honing operation with heavy material removal as achslagenkorrigierende honing operation is performed such that by the honing operation a shift of Hole axis in the direction of the desired position takes place. The honing tool is supported in the radial direction at a distance from the coupling point to the work spindle, wherein at least one cutting group of the honing tool is located between the support point and the coupling to the drive rod.

The said conventional methods for correcting the bore position by honing require considerable effort in the construction of the processing machine and / or the honing tool to make them sufficiently stable against transverse forces occurring during honing. The workpieces can be exposed to considerable forces during processing.

GB 2 419 562 A It discloses a honing method for machining the inner surface of a bore in a workpiece by means of at least one honing operation, wherein in an honing operation an expandable honing tool is used, which in an off-spindle end portion of a tool body an expandable annular cutting group having a plurality of circumferentially distributed around the circumference of the tool body Schneidstoffkörpern whose axial length is smaller than the effective outer diameter of the cutting group with fully retracted cutting material bodies

• a) Ankoppeln des Honwerkzeugs an eine Arbeitsspindel einer Bearbeitungsmaschine; Relative Positionierung (implizit) des Honwerkzeugs und der Bohrung,
• b) Einführen des Honwerkzeugs in die Bohrung mit zurückgezogenen Schneidstoffkörpern bis in eine Einfuhr-Endposition, in welcher sich die Schneidgruppe in einem eintrittsfernen Endbereich der zu bearbeitenden Länge der Bohrung befindet,
• c) und d) Drehen des Honwerkzeugs und gleichzeitiges Expandieren der Schneidgruppe an oder im Bereich der Einfuhr-Endposition bis in eine erste Radialposition der Schneidstoffkörper derart, dass durch materialabtragenden Eingriff von Schneidstoffkörpern an der Innenseite der Bohrung im Endbereich der Bohrung eine zylindrische Erweiterung bis der gewünschte Durchmesser erreicht wird und die Oberflächenrauheit beseitigt wird,
• e) Herausziehen des Honwerkzeugs aus der Bohrung bei gleichzeitiger Drehung des Honwerkzeugs derart, dass die Bohrung ausgehend von der zylindrischen Erweiterung sukzessive in Richtung der Eintrittsseite erweitert wird.

The honing process has the following steps:

• a) coupling the honing tool to a work spindle of a processing machine; Relative positioning (implicit) of the honing tool and the hole,
• b) inserting the honing tool into the hole with the cutting material bodies withdrawn to an import end position, in which the cutting group is located in an entry-distant end area of the length of the hole to be machined,
• c) and d) rotating the honing tool and simultaneously expanding the cutting group at or in the region of the import end position to a first radial position of the cutting material body such that by material-removing engagement of cutting bodies on the inside of the bore in the end of the bore a cylindrical extension to the desired diameter is achieved and the surface roughness is removed,
• e) pulling out of the honing tool from the bore with simultaneous rotation of the honing tool such that the bore is widened starting from the cylindrical extension successively in the direction of the inlet side.

TASK AND SOLUTION

It is an object of the invention to provide a honing method for fine machining an inner surface of a bore in a workpiece, which allows a bore to be machined with relatively little design effort in the design of the processing machine and / or the honing tool so that when needed by honing a correction of the bore position can be achieved. In particular, a position-correcting machining of relatively unstable workpieces without permanent deformation of the workpieces is to be made possible.

To solve these and other objects, the invention provides a honing method having the features of claim 1. Advantageous developments are specified in the dependent claims. The wording of all claims is incorporated herein by reference.

The honing method includes a honing operation using an expandable honing tool having an expandable annular cutting group with a plurality of cutting bodies distributed around the circumference of the tool body in a distal end portion of a tool body, wherein an axial length of the cutting tool body is smaller than the effective outer diameter of the tool body annular cutting group with completely retracted Schneidstoffkörpern. Such a honing tool is referred to as "ring tool" in the context of this application.

The honing tool is rigidly coupled to a work spindle of a processing machine, wherein the coupling can be done directly or with the interposition of a rigid drive rod. The coupling takes place so that the tool axis (longitudinal center axis, rotation axis) is coaxial with the spindle axis of the work spindle. Due to the rigid coupling this orientation is maintained even when exposed to lateral forces on the honing tool.

The honing tool and the bore are positioned relative to each other so that the tool axis of the honing tool is coaxial with the desired position of the bore axis of the bore. This can be done by transverse movements of the work spindle in a plane perpendicular to the spindle axis and / or by transverse movements of the workpiece containing the bore in a plane perpendicular to the bore axis.

In an insertion operation, the honing tool is introduced into the bore with partially or completely retracted cutting bodies to an import end position, in which the cutting group is located in an entry remote end portion of the length of the bore to be machined. The cutting material bodies are pulled back so far that they touch the bore inner wall at any point during insertion. The relative positioning of the honing tool with respect to the bore can take place before or after the insertion operation or overlapping in time.

At the end of the insertion operation, the axially relatively narrow annular cutting group is located in the entry-distant end region, which can lie, for example, in a blind hole directly or with only a small axial distance in the vicinity of the bottom of the hole.

In a subsequent expanding operation, the honing tool is rotated about its tool axis, and at the same time, the annular cutting group is expanded so that its effective outer diameter gradually increases. The expansion or expansion is continued until the cutting material body reach a first radial position such that generated by material-removing engagement of cutting bodies on the inside of the bore in said end portion of the bore substantially centered to the desired position of the bore axis cylindrical extension of the bore has been. The cutting material body dig due to the tool rotation and the simultaneous expansion (increase in diameter) of the cutting group at least on a part of the circumference of the bore to be machined in the bore wall, so that the cylindrical extension is formed. Since the honing tool rotates coaxially with the tool axis in the expansion operation, which in turn is located at the location of the target position of the bore axis, the cylindrical extension of the bore is generated so that its center coincides with the desired position of the bore axis.

After completion of the expansion operation, during which the cylindrical extension is generated, takes place in a pulling operation, pulling the honing tool from the bore with simultaneous rotation of the honing tool such that the bore is widened starting from the extension successively in the direction of the inlet side of the bore. This will achieve that the hole is centered after complete removal of the honing tool from the bore to the bore axis, so the desired position is present.

In this procedure, starting from an optionally not centered, not properly oriented and / or not circular cylindrical shaped bore form before the honing operation, a circular cylindrical bore can be produced whose bore axis lies exactly at the desired position of the bore axis and has the desired angular position. The honing operation can thus change the position of the bore and correct it in the direction of the desired position.

Depending on the magnitude of the deviation of the bore position before the start of the honing operation, relatively strong transverse forces (forces with components perpendicular to the tool axis) can occur between the honing tool and the workpiece or bore wall, and it may be necessary to remove material unevenly over the circumference of the honing tool. These transverse forces act when pulling the honing tool from the bore relatively strong straightening forces, which act due to the tensile load in the direction of the desired position of the honing tool, so that would like to center the honing tool itself in the pulling operation. As a result, the precision in the bore centering can be improved. In addition, a less rigid machine design is required than in those cases in which honing tools are introduced in bore-correcting honing operations with material removal from the input side in the not optimally positioned hole. In addition, the process of producing the centered bore begins in the region of the cylindrical extension, that is to say at the end remote from the region of the bore to be machined. In this area, bores are often connected to the rest of the material of the workpiece, so that the bore or the workpiece material in this area can not avoid even with unstable workpiece structures when creating the cylindrical extension and permanent workpiece deformation can be avoided.

The axially narrow design of the cutting group, so their relative to the outer diameter short axial extent, contributes to the fact that only relatively small lateral Auslenkkräfte occur and only at a relatively short distance or only a small axial length. The design with annular cutting group also means that at relatively low pressure forces large cutting performance can be achieved and that the paths for the removal of removed material, ie of abrasion, are relatively short. Thereby clogging of the abrasive cutting surfaces of the cutting body can be avoided by abrasion and the cutting body remain permanently schneidfreudig. Due to the short design, a better cooling lubricant supply is possible than with longer honing stones, which in turn makes it possible is created to operate the honing tool for material removal at relatively high speeds, so that more removal can be achieved at lower cutting forces.

An annular cutting group is characterized in comparison to conventional honing stones inter alia by the fact that in the covered by the annular cutting group substantially more contact surface between Schneidstoffkörpern and bore inner surface than in a comparatively narrow axial portion of a conventional honing tool with relatively narrow honing stones. According to the claimed invention, more than 60% of the circumference of the annular cutting group is coated with cutting means, in particular even more than 70% or more than 80% of the circumference of the cutting group.

The axial length of the cutting material body can be, for example, less than 30% of the effective outer diameter of the honing tool, in particular between 10% and 20% of this outer diameter. For honing tools for machining typical cylinder bores in engine blocks for cars or trucks, the axial length may be in the range of 5 mm to 20 mm, for example. For example, based on the bore length of a bore to be machined, the axial length may be less than 10% of that bore length.

According to the claimed invention honing tools are used in which the cutting bodies are designed as circumferentially wide and axially narrow Honsegmente, wherein measured in the axial direction axial length of the Honsegmente is smaller than the measured width in the circumferential direction. A hearing segment is usually rigid in itself, so that the entire hearing segment as a whole is moved during delivery. A hearing segment may define an uninterrupted cutting surface, but the cutting surface may possibly also be interrupted once or several times.

If at least three honing segments are provided, the machining forces can be distributed well and relatively evenly over the circumference of the cutting group over the entire effective outer diameter of the honing tool available through expansion. For example, in the cutting group exactly three, exactly four, exactly five or exactly six honing segments of the same or different circumferential width can be provided. Although more than six honing segments within a cutting group are possible, they make the design more complicated and are generally not required. In some cases, it may also be sufficient if the honing tool only has two honing segments.

Preferably, the honing tool is constructed so that the cutting material body can be delivered radially, so that the cutting material body, for example, when expanding the cutting group be delivered radially (perpendicular to the tool axis). Due to the radial deliverability, ie a displacement of the Honsegmente in the radial direction during the delivery, it can be achieved that the engagement conditions between cutting material body and bore inner surface remain virtually constant regardless of the set diameter. By avoiding Schneidstoffkörper tilt during radial delivery uneven wear can be avoided.

In some embodiments, the cutting material bodies form a wedge-shaped cutting surface, wherein a circumferential width of the cutting surface is wider at a spindle-near side than at a spindle-distal side. The cutting material bodies are thus wider on the side which first engages in the removal of the honing tool in the material to be removed, which can be counteracted to a certain extent a necessarily uneven wear.

For a position-correcting effect of the honing process, it is usually useful if the enlargement is generated so that a difference in diameter between the cylindrical extension and a subsequent, (not) not widening bore portion after the generation of the cylindrical extension or before the beginning of the pulling operation at least 100 microns. Preferably, the difference in diameter is at least 200 microns, where it may for example be between 200 microns and 500 microns. Thus, in a pulling operation, a substantial allowance in the range of one or more tenths of a millimeter (in diameter) in an upstroke, i. a stroke in the direction of the inlet opening, be removed. If necessary, rough position errors of the bore can also be corrected.

So that the honing tool can center itself largely without external transverse forces to the desired position of the bore before the start of the pulling operation, it is provided in some embodiments that after the generation of the cylindrical extension before the extraction of a relief operation to relieve the honing tool is performed. Preferably, during the unloading operation, the cutting material bodies are returned, starting from the first radial position, by a predefinable return amount to a second radial position, wherein the return amount may be, for example, between 10 μm and 15 μm. In this case, the radially outer cutting surfaces of the cutting material body may possibly solve from direct engagement with the inside of the cylindrical extension, so that the honing tool due to any residual elasticities on the drive side (work spindle, possibly drive rod) can move even in the centric position of which then starts the following train operation. Alternatively or additionally, a relief could also be achieved by introducing the honing tool axially a few micrometers.

In some process variants, the honing tool is merely expanded during the expansion operation and the cutting group remains at the import end position without being moved axially. In other variants of the method, a short-stroke axial oscillation movement is superimposed at least in phases during expansion of the cutting group to produce the extension of the rotation of the honing tool. As a result, the material removal can be reinforced. Short stroke lengths, for example in the range of 2 mm to 3 mm, are usually sufficient for this purpose.

In the expansion operation, which leads to the generation of the cylindrical extension, is generally carried out with relatively high tool speeds of several hundred min ^-1 , especially at speeds of 500 min ^-1 or more, for example in the range between 500 and 2000 min ^-1 . High speeds are generally conducive to still achieve high material removal per unit time at relatively low cutting forces.

In order to achieve sufficient removal of material during withdrawal of the honing tool, without excessively prolonging the cycle times of the process, it has proven to be advantageous if up to 2 m / s is used when pulling out the honing tool at a lifting speed in the range of 0.1 m / s , in particular in the range of 0.3 m / s to 0.7 m / s. Optimum values within these ranges can be determined by a few tests depending on the material, the cutting means and possibly other parameters. For some materials, it may be that smaller lifting speeds are needed or higher lifting speeds are possible.

In most process variants honing tools are used, in which the cutting material body cutting grains having a mean grain size in the range of 50 microns to 250 microns. With grain sizes in this range, a sufficiently efficient removal of material is generally possible, wherein at the same time the resulting after pulling the honing tool surface structures are optimized so that subsequent processing stages, in particular by honing, only have to afford a small material removal.

In some variants of the method, an expandable honing tool with relatively long honing stones, the length of which is significantly larger than its width in the circumferential direction, is used in one of the position-correcting honing operations following another honing operation. It can be a conventional long stroke honing tool. The length of the honing stones may be, for example, more than 30% or more than 40% of the length of the bore. As a result, if necessary after the position correction, the cylinder shape of the bore can be improved by honing.

The processing machine may be a honing machine specially set up for honing processes, but possibly also another suitably equipped machine tool, for example a machining center or a grinding machine. The workpiece to be machined is received and held by a workpiece holding device of the processing machine.

In order to set the honing tool for a honing operation in his working movement, the work spindle is rotated by means of a rotary drive to the associated spindle axis. The axial stroke movement superimposed on the rotation relative to the machined workpiece can be produced in different ways. In many cases, the workpiece does not move during machining in the axial direction, while the rotational movement and the lifting movement are generated by corresponding rotation and lifting movement of the working spindle of the machine tool and transferred to the honing tool (axially stationary workpiece). It is also possible to bring about the lifting movement by means of a translatory movement of the workpiece with an axially stationary work spindle or by a coordinated combination of axial movements of the workpiece and work spindle. For this purpose, the processing machine has at least one lifting drive for generating an axial lifting movement of the work spindle and / or the workpiece holding device parallel to the spindle axis.

The honing tool described in this application and its variants described can be taken alone, i. regardless of the procedure, be protected.

BRIEF DESCRIPTION OF THE DRAWINGS

• Fig. 1 eine schematische Ansicht eines Teils einer mehrachsigen Bearbeitungsmaschine in Form einer Honmaschine bei der Durchführung einer Ausführungsform des Honverfahrens;
• Fig. 2 in Fig. 2A einen axialen Schnitt und in Fig. 2B einen Querschnitt durch eine Ausführungsform eines Honwerkzeugs mit einer ringförmigen Schneidgruppe;
• Fig. 3 verschiedene Phasen einer positionskorrigierenden Honoperation.

Further advantages and aspects of the invention will become apparent from the claims and from the following description of preferred embodiments of the invention, which are explained below with reference to the figures. Showing:

• Fig. 1 a schematic view of a part of a multi-axis processing machine in the form of a honing machine in carrying out an embodiment of the honing process;
• Fig. 2 in Fig. 2A an axial section and in Fig. 2B a cross-section through an embodiment of a honing tool with an annular cutting group;
• Fig. 3 different phases of a position-correcting honing operation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In Fig. 1 FIG. 3 is a schematic view of a portion of an NC controlled multi-axis processing machine 100 in the form of a honing machine 100 in the direction parallel to the x-direction of the machine coordinate system MKS. The honing machine has several honing units arranged side by side in the x-direction and simultaneously operable. In Fig. 1 some components of a honing unit 110 are shown. A control device 115 controls working movements of movable components of the honing machine.

The honing machine is adapted for honing cylinder surfaces in the manufacture of cylinder blocks for internal combustion engines. A currently machined workpiece 120 is clamped on a workpiece holding device 125 fixed. The position of the workpiece on the workpiece holding device is predetermined by means of indexing elements 126, so that a defined relationship exists between the workpiece coordinate system WKS and the machine coordinate system MKS. The workpiece holding device has a horizontally movable carriage 127, which can be moved by means of a controllable via the controller 115 drive 128 parallel to the y-direction of the machine coordinate system MKS.

The workpiece is in the example a cylinder crankcase of a 4-cylinder in-line engine with four axis-parallel cylinder bores. The next to be machined hole 122 can be seen, the other holes are offset in the x direction.

The honing unit 110 is attached to the front of a vertical support structure 105 mounted on the machine bed of the honing machine. The honing unit comprises a headstock 135, which serves as a bearing for the work spindle 130, which is guided with a vertical spindle axis 132 in the headstock. The rotation of the work spindle about the spindle axis is effected by a rotary drive, not shown, mounted on the headstock and e.g. acts on the work spindle via a chain drive. A lifting drive structurally connected to the headstock causes the vertical movements of the work spindle parallel to the spindle axis 132 during insertion of the honing tool 200 to be machined into the bore to be machined or when removing the honing tool from this bore. In addition, the lifting drive can be controlled during honing by the control device 115 so that the honing tool within the bore of the workpiece performs a vertical reciprocating motion according to the desired Honparameter.

The honing tool 200 is rigidly coupled to the free end of the work spindle 130 in the example. For the production of the rigid but detachable connection between work spindle and honing tool For example, a correspondingly secured bayonet connection, a screw connection, a flange connection or a conical connection, for example with hollow shaft taper (HSK), may be provided. Neither in the work spindle nor in the honing tool a joint is provided. The central tool axis 212 of the honing tool runs in the unloaded state, ie in the absence of transverse forces acting on the honing tool, coaxially with the spindle axis 132 in the region of its bearing in the headstock.

The honing unit 110 with the vertical work spindle 130 contained therein is linearly movable in a horizontal direction parallel to the x-axis of the machine coordinate system MKS, ie perpendicular to the spindle axis in a transverse direction. Thereby it is u.a. possible, without moving the workpiece on a workpiece first to edit a first bore, then retract the work spindle to move the honing unit as a whole in a transverse movement parallel to the x-direction and to position approximately coaxially to a second bore to be machined to the same honing unit to edit the second hole. Horizontal transverse movements in the x direction can also be used to move the honing unit to a tool changer arranged in line with the transverse movement. In order to enable the horizontal transverse movement, the headstock is mounted on a horizontally movable carriage 114 which is guided linearly on two horizontal guide rails on the front of the support structure 105 facing the headstock. The transverse movement is effected by a positioning drive 118 disposed between the support structure and the carriage 114.

In the honing operation described in more detail below, a honing tool 200 of special construction is used, which in this application is also referred to as an "annular tool" (cf. Fig. 2 ). The honing tool has a cutting group 220 mounted annularly on the tool body 210 with cutting material bodies 220-1 to 220-3 distributed around the circumference of the tool body, which can be delivered or retracted in the radial direction by means of an associated feed system. The cutting material bodies are designed as Honsegmente whose width in the circumferential direction is significantly greater than their length in the axial direction. The abrasive cutting material bodies responsible for material removal on the workpiece are concentrated in an axially relatively narrow zone (annular cutting group) and occupy a relatively large portion of the circumference of the honing tool.

Fig. 2 2A shows a longitudinal section through an embodiment of an annular tool 200 with a single annular cutting group 220 and simple expansion. Fig. 2B shows a cross section through the cutting group The ring tool 200 has a tool body 210, which defines a tool axis 212, which at the same time the axis of rotation of the ring tool while honing is. At the spindle end of the ring tool (in Fig. 2A Above) is a non-illustrated coupling structure for rigidly coupling the ring tool to a drive rod or a work spindle of a honing machine or other machine tool, which has a work spindle which is both to the spindle axis rotatable and parallel to the spindle axis oscillating back and forth movable ,

At the spindle end facing away from the tool body (in Fig. 2A below) is the annular cutting group 220, which has several (in the example, three) evenly distributed over the circumference of the tool body Schneidstoffkörper 220-1, 220-2, 220-3, which delivered by means of a Schneidstoffkörper-delivery system radially to the tool axis 212 to the outside can be used to press the abrasive outer sides of the Schneidstoffköpers, ie the cutting surfaces, with a defined pressing force or pressing force against the inner surface of a bore to be machined. Each of the three curved cutting material body is designed as a very wide in the circumferential direction, in contrast, in the axial direction against narrow Honsegment which covers a circumferential angle range between 115 ° and 120 °. The honing segments are decoupled from the tool body and displaceable radially relative to the tool axis 212. The ring formed by the honing segments terminates flush with the tool body on the side facing away from the spindle, so that the ring is seated completely inside the spindle-remote half of the tool body at the end of the ring tool facing away from the spindle.

A flush termination with the lower end of the tool body is cheap, but not mandatory. In general, the ring should sit in the spindle distal third or in the distal quarter of the tool body, there may be a small distance to the front side of the tool body.

The axial length LHS of the Honsegmente is less than 15%, in particular less than 10% of the bore length L. The Honsegmente are about 4 mm to 35 mm, in particular about 10 mm high (in the axial direction), which in the example between 5% and 30%, in particular between 10% and 20% of the effective outer diameter of the cutting group corresponds to maximally inwardly drawn cutting bodies. The honing tool has only this one annular cutting group. The axial length LHS therefore simultaneously corresponds to the axial length of the entire cutting region of the honing tool.

Each cutting material body is fixed to an outside of an associated support bar 224-1, 224-2 made of steel by soldering. Alternatively, the cutting material body can also be attached by gluing or by screws, whereby an easier replacement is possible. each Support bar has on its inner side an inclined surface which cooperates with a conical outer surface of an axially displaceable Zustellkonus 232 in such a way that the support bars are delivered with the carried cutting material bodies radially outward when the Zustellkonus means of a machine-side feed device against the force of return springs 234 , 226, 228 is pressed in the direction of the spindle facing away from the end of the ring tool. In the case of an opposing feed movement, the carrying strips with the honing segments are retrieved radially inward with the aid of circulating return springs 226, 228. The radial position of the cutting material body is thereby controlled without play on the axial position of the Zustellkonus 232.

A hearing segment may, as shown, have on its outside a continuous, uninterrupted cutting surface. For this purpose, the cutting coating consist of a single piece of the cutting means. It is also possible that a plurality of (eg, two, three, four, five, six, or more) relatively narrow cutter bodies are mounted closely adjacent, with or without mutual spacing, to the arcuately curved outside of a common carrier member. The cutting surface would then be interrupted, which may possibly be favorable for the cooling lubricant supply.

The use of relatively wide honing segments in the annular cutting group may i.a. be favorable in the machining of bores, e.g. have for the purpose of gas exchange transverse bores, which open at the bore surface to be machined. Wide, rigid hearing segments can bridge the mouth area, so that the honing tool can not "get stuck". If only a few (for example three) wide honing segments are provided, only a small number of radial perforations must be provided on the tool body, resulting in improved mechanical stability, which is favorable in the case of position-correcting machining in order to withstand transverse forces.

This machine and tool concept enables a position-correcting material-removing machining of the inner surface of the bore 122 in order to bring the bore position within the tolerances into its desired position by means of honing.

An embodiment of a suitable method will be described with reference to FIG Fig. 3 explained in more detail. Fig. 3 shows different phases or different sub-operations of a position-correcting honing operation. As in Fig. 1 shown schematically, the bore 122 is not yet at its desired target position after the previous processing steps, which is represented in the example by the target position SB of the bore axis. Rather, the bore 122 still shows a lateral offset to the desired position, wherein the actual position of the Bore (characterized by the current bore axis IB) is outside the tolerances next to the desired position. In addition, the bore inner surface does not yet show the intended intended use surface structure, which is also still to produce by honing.

First, in a positioning operation, the honing tool is positioned relative to the bore so that the tool axis 212 is coaxial with the desired position SP of the bore. For this purpose, if necessary, the workpiece carrier 127 is moved horizontally parallel to the y-direction of the machine coordinate system and / or the headstock or the work spindle parallel to the x-direction of the machine coordinate system. The coaxial position set by the positioning operation is in Fig. 1 and Fig. 3A shown schematically.

Before, after or simultaneously with the positioning, the feed rod of the cutting material delivery system is moved upward until the cutting bodies assume their maximum retracted position, whereby the outer diameter of the annular cutting group assumes its smallest value. The honing tool will then fit into the hole in vertical operation without touching the bore walls.

Thereafter, the honing tool is inserted into the bore 122 by actuation of the lifting drive of the work spindle and lowered until the honing tool reaches an import end position in which the annular cutting assembly 220 is located in an entry distal end portion 123 of the bore 122 ( Fig. 3B ). The end region remote from the bore inlet 124 defines the lower end or the far end of the overall length of the bore interior to be machined. Since in the ring tool shown the cutting group 220 is flush with the spindle distal end face of the tool body, the ring tool can be practically driven up to the stop on the bottom of the hole or, in through holes, to the stop on the top of the workpiece holder. In practice, however, a small distance of a few millimeters, for example 1 to 2 mm, is generally complied with. During the insertion operation, the work spindle can be rotated slowly, but this is not absolutely necessary.

When the honing tool is in the import end position, the subsequent part operation, an expanding operation, may begin. In the expansion operation ( Fig. 3C ), the honing tool is rotated about its tool axis and at the same time the cutting group is slowly expanded by driving the Schneidstoffkörper-delivery system, so that the effective outer diameter of the cutting group gradually increases. If the hole in the remote end portion not already to the desired position of the bore axis is centered and has a circular cross-section, in a certain phase of the expansion operation, first a unilateral material engagement, ie an abrasive machining in partial section in that area of the bore inner surface takes place, which is radially closest to the desired position of the bore axis. With increasing effective outer diameter of the cutting group then the partial section is gradually in a full cut, in which over the entire circumference of the cutting group material is removed.

The radial delivery of the cutting material body to the outside is continued until the cutting material body reach a predefined first radial position ( Fig. 3C ). Thereafter, the further delivery is stopped by the control device. By the removal of material over the circumference of the cutting group in conjunction with the radial feed, a cylindrical extension 121 is generated in the expansion operation by material-removing engagement of cutting bodies on the inside of the bore in the end portion 123 of the bore, which is usually within the tolerances of the exact Target position of the bore axis is centered. If the hole is not precisely positioned, the cylindrical extension will still be decentered from the current hole axis. The excess of the extension with respect to the hole section subsequent bore section is usually at least 100 microns in relation to the diameter. In most cases the values are higher, for example at 200 μm or more or at 400 μm or more.

Experiments have shown that during the expansion operation speeds of the honing tool in the range of 400 min ^-1 to 1000 min ^-1 usually bring good results. In one case, was carried out with approximately 500 min ^-1 using oil as a cooling lubricant.

In a variant of the method, the honing tool remains at the set axial position during the expansion operation, so that no lifting movement is superimposed. In other variants of the method, the lifting drive of the work spindle is actuated at least in phases during the expansion operation in order to superimpose an axially short-stroke oscillatory movement on the rotational movement of the honing tool during radial expansion. As a result, possibly more favorable material removal conditions can be achieved. The axial length of the cylindrical extension produced would then be somewhat larger than with only radial expansion without superimposed lifting movement.

In a variant of the method, after the end of the expansion operation, ie when the cutting material body has reached the first radial position, the honing tool is relieved in a relieving operation which returns the cutting material bodies to a second radial position by a specific return amount of, for example, 10 to 15 μm become. As a result, the physical contact between the outer surface of the Honsegmente and the bore inner wall is canceled, so that the honing tool may even better under the influence of elastic forces from the work spindle centered in relation to the spindle axis. This step can also be omitted.

After completion of the expansion operation and, if necessary, after the unloading operation, a traction operation ( Fig. 3D ), in which the rotationally driven honing tool with a suitable lifting speed is slowly pulled out of the bore in the direction of the bore entry. This results, starting from the bottom of the hole, a gradual extension of the cylindrical extension centered on the desired position of the bore axis, so that the bore, as it were, receives from the bottom of the hole its circular cylindrical bore shape centered on the desired position of the bore axis. After complete removal of the honing tool from the hole ( Fig. 3E ) the hole is centered in full length with respect to the desired position of the bore axis. Also, the angularity of the hole is set correctly, so that the bore axis is oriented for example perpendicular to the top surface.

For the partial operation of pulling out the honing tool (with simultaneous axial enlargement of the cylindrical extension), the lifting speeds are typically in the range between 0.3 m / s and 0.7 m / s, but they may also be smaller, for example, down to 0.1 m / s, or but larger, to over 1 m / s, for example up to about 2 m / s.

In some cases it may be sufficient to perform these honing operations (including insertion of the honing tool, expanding to create a cylindrical extension, pulling out) only once. However, it is also possible to repeat these steps once or several times, which may be particularly advantageous if the position error of the bore is relatively high prior to the first machining and / or if it is desired in the pulling operation only a smaller material removal than to produce the final required.

After the position-correcting honing operation, further machining operations may follow. In some variants of the method, at least one further honing operation is subsequently carried out with the aid of a conventional expandable honing tool 300, which is coupled to the work spindle once or several times and has relatively long honing stones 320 whose length can amount, for example, to more than 30% of the length of the bore ( Fig. 3F ). As a result, any remaining cylinder shape errors and / or other shape errors can still be corrected.

The process can be performed with vertical axial direction as shown. Even a horizontal machining is possible. The hole can, as shown, be uncoated, so that directly the base material of the workpiece is removed. A machining of coated holes is also possible, in which case the material of the coating would be removed.

An annular tool may optionally have a separately deliverable further ring with cutting material bodies in addition to the spindle-distal ring.

It may also be possible to use a fine boring tool for a similar material-removing, position-correcting, finishing process instead of a ring tool configured for honing, which has at least one controllable cutting element with geometrically defined cutting edge (instead of an annular cutting group with geometrically indefinite cutting edges) attached end-to-end , Optionally, at least one pair of diametrically opposed controllable cutting elements may be present. The method steps: inserting the fine boring tool, expanding or retracting the cutting element while rotating to produce a cylindrical extension, pulling out with extended cutting element with simultaneous rotation could be carried out analogously to the procedure described.

Claims (13)

1. Honing method for machining the inner surface of a bore (122) in a workpiece (120) by means of at least one honing operation, in particular for honing cylinder running surfaces in the production of cylinder blocks or cylinder liners for reciprocating piston engines,
   wherein in a honing operation an expandable honing tool (200) is used, having in an end region of a tool body that is remote from the spindle an expandable, annular cutting group (220) with a number of cutting material elements which are distributed around the circumference of the tool body and the axial length of which is less than the effective outside diameter of the cutting group with the cutting material elements fully retracted,
   wherein the cutting material elements are configured as honing segments (220-1, 220-2, 220-3) that are wide in the circumferential direction and narrow in the axial direction such that an axial length of the honing segments, measured in the axial direction, is less than the width measured in the circumferential direction, and
   wherein on the annular cutting group (220) more than 60% of the circumference is covered with cutting means,
   comprising the following steps:

   rigid coupling of the honing tool to a working spindle of a machine tool;

   relative positioning of the honing tool and the bore in such a way that a tool axis (212) of the honing tool is coaxial with a target position (SB) of the bore axis of the bore;

   inserting of the honing tool into the bore with the cutting material elements retracted, until it is in a final insertion position, in which the cutting group is located in an end region (123) of the length to be machined of the bore that is remote from the inlet;

   turning of the honing tool and simultaneous expanding of the cutting group at or in the region of the final insertion position into a first radial position of the cutting material elements in such a way that a cylindrical widening (121) of the bore that is substantially centered in relation to the target position of the bore axis is created by the material-removing engagement of cutting material elements on the inner side of the bore in the end region of the bore;

   withdrawing of the honing tool from the bore with simultaneous turning of the honing tool in such a way that, from the cylindrical widening, the bore is successively widened in the direction of the inlet side.
2. Honing method according to claim 1, characterized in that a honing tool having at least one of the following properties is used:

   (i) on the annular cutting group (220) more than 70% or more than 80% of the circumference of the cutting group is covered with cutting means;

   (ii) the axial length (LHS) of the cutting material elements is less than 30% of the effective outside diameter of the cutting group, in particular between 10% and 20% of this outside diameter;

   (iii) the axial length (LHS) of the cutting material elements lies in the range of 5 mm to 20 mm;

   (iv) the axial length (LHS) of the cutting material elements is less than 10% of the bore length of the bore.
3. Honing method according to claim 1 or 2, characterized in that the cutting group has at least three honing segments (220-1, 220-2, 220-3).
4. Honing method according to claim 3, characterized in that in the cutting group three, four, five or six honing segments of the same circumferential width or of different circumferential widths are provided.
5. Honing method according to any of the preceding claims, characterized in that a honing tool in which the cutting material elements form a wedge-shaped cutting surface is used, a circumferential width of the cutting surface on a side near the spindle being wider than on a side remote from the spindle.
6. Honing method according to any of the preceding claims, characterized in that a honing tool in which the cutting material elements have abrasive grains with an average grain size in the range of 50 µm to 250 µm is used.
7. Honing method according to any of the preceding claims, characterized in that the cutting material elements are adjusted radially during the expansion of the cutting group (220).
8. Honing method according to any of the preceding claims, characterized in that the widening (121) is created in such a way that a difference in diameter between the widening and an adjoining, non-widened portion of the bore is at least 100 µm, in particular 200 µm or more.
9. Honing method according to any of the preceding claims, characterized in that, after the creation of the cylindrical widening (121), a relieving operation is carried out to relieve the honing tool before the beginning of the withdrawal.
10. Honing method according to claim 9, characterized in that, in the relieving operation, the cutting material elements are returned from the first radial position to a second radial position by a return amount, the return amount preferably being between 10 µm and 15 µm.
11. Honing method according to any of the preceding claims, characterized in that the withdrawal of the honing tool takes place with a stroke rate in the range of 0.1 m/s to 2 m/s, in particular in the range of 0.3 m/s to 0.7 m/s.
12. Honing method according to any of the preceding claims, characterized in that during the expanding of the cutting group to create the widening (121) a short-stroke axial oscillating movement is superposed on the rotation of the honing tool, at least in certain phases, an axial stroke preferably lying in the range of 2 mm to 3 mm.
13. Honing method according to any of the preceding claims, characterized in that an expandable honing tool (300) with honing sticks (320) of which the axial length is greater than their width in the circumferential direction is used in a further honing operation following the position-correcting honing operation, wherein the axial length preferably is more than 30% of the length of the bore.

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